Brain plasticity at the right time and place is of paramount importance during development with lasting consequence throughout life. Just as sensory input in early life shapes primary sensory cortex, emotional experience may shape the limbic-cortical relay system. Fibers from the BLA actively sprout within the mPFC during the post-weanling period, forming increased contacts with GABAergic interneurons as late as the early adult period. This connectivity requires further evaluation ultrastructurally (with Lichtman), and the identity of the receptors at these appositions merits investigation (with Zhuang). Here, we focus on the shift of neural circuit mechanisms from amygdala to mPFC underlying fear extinction across development. Using these stages as a milestone, we will measure developing synaptic inputs onto individual PV-cells of the mPFC by whole-cell recording techniques in slices from PV-EGFP mice crossed to various mouse models. The maturational state of afferents from the BLA in particular, will be examined by optogenetic tagging of this projection. Ultimately, we aim to determine whether dynamic epigenetic regulation (such as by imprinted genes identified by Dulac) dictates the functional maturation of these pivotal cortical inhibitory circuits. Identifying cell-specific mechanisms that underlie epigenetic regulation of critical periods may provide valuable insight into potential circuit-based therapies for pathologies arising from aberrant environment-gene interactions.